1. Field of the Invention
The present invention applies to transmitting apparatus (terminal repeater devices) having a redundant configuration of work and protection lines based on a standard such as a synchronous optical network (SONET), synchronous digital hierarchy (SDH), or the like.
2. Description of the Related Art
Transmitting apparatus (i.e. Optical terminal repeater devices, Optical terminals/transmitting devices, Add/Drop Multiplexer) are increased line capacity by expansion units that including work and protection line.
FIG. 1 illustrates the configuration of an optical terminal in which expansion units accommodating work and protection lines are provided. An optical terminal 1 comprises a main unit 100, and expansion units 90 and 91, and the main unit and the expansion units are configured of separate shelves.
The main unit 100 comprises a work-line setting unit 30, a protection-line setting unit 30′, interface units 71, 72, 73, and 74, a work-timing-clock generating unit 96, and a protection-timing-clock generating unit 96′.
The interface units 71 and 73 are connected to work lines 4 and 4′.
The interface units 72 and 74 are connected to protection lines 6 and 6′.
The interface units 71, 72, 73, and 74 are connected to the work-line setting unit 30 and the protection-line setting unit 30′.
The work-line setting unit 30 and the protection-line setting unit 30′ perform line settings based on the overhead information of the signals received from receiving devices 10, 11, 12, and 13 within the interface units 71, 72, 73, and 74. Further, the work-line setting unit 30 and the protection-line setting unit 30′ output the signal based on the line settings to transmitting devices 20, 21, 22, and 23 within the interface units 71, 72, 73, and 74.
The transmitting devices 20 and 21 output a light signal to the work lines 4 and 4′, and the transmitting devices 22 and 23 output a light signal to each of the protection lines 6 and 6′.
The work-line setting unit 30 and the protection-line setting unit 30′ include a work clock unit 95 and a protection clock unit 95′.
The work clock unit 95 includes a circuit-changing switch 61, and a PLL circuit 65.
The PLL circuit 65 comprises a phase comparator 62, a loop-back filter 63, and a voltage-controlled oscillator 64.
The circuit-changing switch 61 selects a clock from the work-timing-clock generating unit 96 or the protection-timing-clock generating unit 96′, and outputs this to a phase comparator 62.
The phase comparator 62 compares the clock selected by the circuit-changing switch 61 with the clock from the voltage-controlled oscillator 64, and outputs the comparison result to the loop filter 63.
The loop filter 63 converts the input from the phase comparator 62 into a voltage value, and outputs this to the voltage-controlled oscillator 64.
The voltage-controlled oscillator 64 supplies a clock signal to a bus-interface unit 80 and the phase comparator 62.
The bus-interface unit 80 performs transmitting/receiving a signal as to the interface units 71 through 74 in accordance with the line setting, and the expansion units 90 and 90′, and also supplies a clock signal to the expansion units 90 and 90′.
The protection-line setting unit 30′ has the same configuration as the work-line setting unit 30, so the same configurations are appended with a dash on the same numbers thereof, and the descriptions thereof are omitted.
The expansion unit 90 comprises a work-line setting unit 31, a protection-line setting unit 31′, interface units 71′, 72′, 73′, and 74′, an intra-expansion-unit work-timing-clock generating unit 97, and an intra-expansion-unit protection-timing-clock generating unit 97′.
The interface units 71′ and 73′ are connected to work lines 5 and 5′.
The interface units 72′ and 74′ are connected to protection lines 7 and 7′.
The interface units 71′, 72′, 73′, and 74′ are connected to the work-line setting unit 31 and the protection-line setting unit 31′.
The work-line setting unit 31 and the protection-line setting unit 31′ transmit the signals received from receiving devices 10′, 11′, 12′, and 13′ within the interface units 71′, 72′, 73′, and 74′ to bus-interface units 80 and 80′ through bus-interface units 82 and 82′ respectively.
Further, the work-line setting unit 31 and the protection-line setting unit 31′ output the signals transmitted from the bus-interface units 80 and 80′ through the bus-interface units 82 and 82′ respectively to transmitting devices 20′, 21′, 22′, and 23′ within the interface units 71′, 72′, 73′, and 74′ in accordance with the line setting.
The transmitting devices 20′ and 21′ output a light signal to the work lines 5 and 5′, and the transmitting devices 22′ and 23′ output a light signal to the protection lines 7 and 7′ respectively.
The work-line setting unit 31 and the protection-line setting unit 31′ include an intra-line-setting-unit work-clock unit 98 and an intra-line-setting-unit protection-clock unit 98′.
The intra-line-setting-unit work-clock unit 98 comprises a delay line 67, a selecting circuit 68, and a PLL circuit 66.
The clock signal received from the bus-interface unit 82 is input to the each of delay line 67 and the selecting circuit 68.
The selecting circuit 68 selects from the output of the delay line 67 and the output of the bus-interface unit 82, and outputs this to an intra-expansion-unit work-timing-clock generating unit 97 and an intra-expansion-unit protection-timing-clock generating unit 97′.
The delay line 67 sets the amount of retardation based on the steady phase difference from the work timing clock generating unit to the circuit within the expansion unit, which is generated by the entire system.
This amount of retardation is based on the retardation due to the connection between the main shelf accommodating the mounting parts serving as components of the mounting board, and pattern length of the mounting board, the main unit of the optical terminal, and the shelf accommodating the expansion unit.
That is to say, in the event of employing such a device configuration, the delay line 67 of the shelf on the expansion-unit side is for absorbing the phase difference (skew) between the work and protection clock signals which is caused due to mounting pattern length difference, and the solid-state irregularity of the respective mounting parts in the clock route up to the shelf on the expansion-unit side with the work-timing-clock generating unit 96 and the protection-timing-clock generating unit 96′ within the shelf on the main-unit side as the starting point.
The PLL circuit 66 is a circuit for supplying a clock signal to the work-line setting unit 31, and is for synchronizing an internal clock with the clock from the bus-interface unit 82.
The intra-expansion-unit work-timing-clock generating unit 97 includes a switching unit 94, selects the clock from the intra-line-setting-unit work clock unit 98 and the intra-line-setting-unit protection clock unit 98′ within the work-line setting unit 31 and the protection-line setting unit 31′, and supplies this clock to the interface units 71′ through 74′.
The intra-expansion-unit protection-timing-clock generating unit 97′ includes a switching unit 94′, selects the clock from the intra-line-setting-unit work clock unit 98 and the intra-line-setting-unit protection clock unit 98′ within the work-line setting unit 31 and the protection-line setting unit 31′, and supplies this clock to the interface units 71′ through 74′.
Known means for performing the phase synchronization between multiple clock signals include the means disclosed in Japanese Unexamined Patent Application Publication No. 05-2438, and the means disclosed in Japanese Unexamined Patent Application Publication No. 10-240375.
With the related art, it has been necessary for steady phase difference to be generated between the work and protection-timing-clock generating units, and the intra-expansion-unit work and protection-timing-clock generating units needs to be determined beforehand.
That is to say, it has been necessary to determine the amount of retardation of the delay line using the mounting parts and pattern length of the mounting board serving as components in the main unit and expansion unit thereof
Accordingly, with the related art, modifying the system design thereof needs to be performed while maintaining the correlation between the mounting parts and the pattern length on the mounting board, which has provided a problem wherein flexible handling thereof cannot be performed, or the modifiable range thereof is limited.
Further, phase correction using a fixed delay line cannot correct the phase shift due to solid-state irregularity for each mounting part and the amount of propagation delay.